docs: keep example commands in their own working directories

[git-jxj]

Summary

Pasting the example commands in sequence leaves the shell in examples/go, so the next cd examples/rust fails. Run each directory change in a subshell and state that the examples start from the repository root.

Scope Check

• Stays within the v0.1 bundled-skill installer boundary.
• Does not add marketplace, registry, private remote install, script execution, GUI, MCP server, or agent runtime behavior.
• Updates golden cases for observable installer behavior changes. Not applicable: only the documented shell commands change.
• Regenerates host constants after spec/hosts.json changes. Not applicable: the host spec is unchanged.

Verification

• make check (including the four SDK examples)
• Bash directory-navigation check fails on the old snippet and passes with the subshells; the final working directory remains the repository root.
• bash -n and git diff --check

[samzong]

/approve